After coming into this information age, photochemical polymerization has been widely used in various fields beyond that of synthetic resins, and there has been being extensively used even in the fields of information recordings and electronic equipments such as paints, lithographic plates for printing, printing circuits, and integrated circuits. Photochemical polymerization is a technique for polymerizing polymeric compounds by irradiating lights and it is roughly classified into (i) photopolymerization that initiates the polymerization of polymeric compounds by directly irradiating them to be activated, and (ii) photosensitization polymerization that polymerizes polymeric compounds by irradiating them in the presence of photosensitizers to make them into their growth-active forms. In both cases, as characteristic features, the initiation and the suspension of polymerization can be controlled by flashing excited light sources, and the rate and the degree of polymerization can be easily controlled by appropriately selecting the strength and the wavelength of the light sources. The photochemical polymerization can be proceeded even at a relatively low temperature condition because it requires only a lesser beam energy for initiating its polymerization. Due to the above advantageous features of photochemical polymerization, in the field of information recordings such as holography and lithographic plates for printing, and photopolymeric compositions, those which can be polymerized by irradiating visible lights such as those of argon ion lasers, helium ion lasers, and second harmonics of Nd-YAG lasers have been rapidly increased in demand.
However, most of polymeric compounds and polymerization initiators, which are incorporated into photopolymeric compositions, absorb ultraviolet rays only, and this inevitably needs photosensitizes as a technical factor when the photopolymeric compositions are polymerized by visible lights. The properties requisite for polymerization initiators are to have a relatively large molecular absorption coefficient (hereinafter may be abbreviated as “ε”), photosensitize various polymeric compounds, have a relatively high sensitization efficiency, have a desired solubility and compatibility with other ingredients, and have a satisfactory stability. Representative examples of such photosensitizes are, for example, melocyanine dyes disclosed in Japanese Patent Kokai No. 151,024/79, cyanine dyes disclosed in Japanese Patent Kokai No. 29,803/83, stilbene dyes disclosed in Japanese Patent Kokai No. 56,403/84, coumarin dyes disclosed in Japanese Patent Kokai No. 23,901/88, methylene blue derivatives disclosed in Japanese Patent Kokai No. 33,104/89, and pyrane derivatives disclosed in Japanese Patent Kokai No. 329,654/94. These compounds have both merit and demerit, and there has not yet been found any photopolymeric compound, comprising a polymeric compound and a binding resin, which does exert the above identified properties. Because of this, in a novel field to which photopolymeric compounds are applicable, for example, in the fields of information recordings and electric equipments, it is usual that, depending on use, materials suitable for polymeric compounds, binders, etc., other than photosensitizes, are firstly selected, and then, among various organic compounds, appropriate ones for such polymeric compounds and polymerization initiators are screened in such a manner of trial and error.
In the field of information displays, electroluminescent elements (hereinafter abbreviated as “EL elements”) are now highlighted as a display element for the forthcoming generation. At present, cathode-ray tubes are predominantly used in relatively large-sized information displays such as computer termini and TV receivers. The cathode-ray tubes, however, are relatively large in mass and weight and relatively high in operation voltage, and this hinders their applicability for commonly used equipments and small-sized portable ones whose transportability is highly valued. More required are the information displays for small-sized equipments, which have a thinner and lighter plain-form and operate at a lower operation voltage and wattage. Due to advantageous features of relatively low operation voltage and wattage, liquid crystal elements are now commonly used in many fields. However, the information display equipments equipped with such liquid crystal elements will change in contrast depending on their view angles; information are clearly displayed only when viewed within a specific view angle and usually require blacklight, resulting in a problem that they could not be reduced in wattage as much as they are expected. As a display element to overcome these drawbacks, there appeared an electroluminescent element, i.e., an organic EL element.
Organic EL element is a luminous element which generally comprises an inserted luminous layer containing a luminous compound placed between a cathode and an anode, and which utilizes luminescence such as fluorescence or phosphorescence emitted from the luminous compound in such a manner that a dc voltage is energized between the cathode and the anode to supply both positive holes and electrons to the luminous layer to rebind them together to make the luminous compound into its excited state, and the excited luminous compound returns to its ground state while emitting luminescence. As characteristic features, organic EL element can be appropriately changed its luminous color tint by selecting an appropriate organic compound as a host compound and altering a dopant as a guest compound used with the host compound. Depending on the combination of the host and the guest compounds, the luminescent brightness and the life expectancy of organic EL element can be possibly improved by a large margin. It is said that organic EL element is a theoretically excellent luminous element because it autonomously emits light and has a relatively low operation wattage as disclosed, for example, in “Organic Photonics”, edited by Hiroyuki SASABE, pp. 136-160, Mar. 20, 1995, published by Agne Shofusha, Kabushiki Kaisha, Tokyo, Japan, and The Journal of the Institute of Electronics, Information and Communication Engineers, Yoshinori SAITO, Vol. 84, No. 11, pp. 767-774, 2001.
Most of the organic EL elements conventionally proposed, however, are relatively low in tolerance and, as a demerit, they have a problem of being easy reduced in brightness within a relatively short period of time when used under severe conditions, for example, when they are used in automobiles that are unavoidable from vibrations and high temperatures.
In view of these circumstances, the object of the present invention is to provide novel organic compounds having an absorption and luminescent maxima in the visible region and widens the variety of selectable light absorption agents and luminous agents in producing polymeric compositions.
Another object of the present invention is to provide organic materials useful in organic EL elements pursuing high durability.